Mangrove zooplankton of North Queensland, Australia

Abstract

Measurements of plankton community structure and trophic resourcespotentially available to planktonic copepods were made in the mangroveestuaries of six rivers in Northeastern Australia. The Pascoe, Claudie,Lockhart, McIvor and Daintree Rivers represent wet tropical systems on CapeYork, whereas the Haughton River estuary has restricted freshwater inflowbecause of a drier climate and freshwater diversion for agriculture. TheHaughton River was sampled approximately monthly between October 1992 andMay 1994, and had a mean abundance of zooplankton >37 µm of 200l⁻¹ (range 60–500 l⁻¹). The Cape Yorkrivers were sampled infrequently, and zooplankton abundances ranged between0.4 and 1400 l⁻¹. The zooplankton of all rivers was dominatedby copepods, particularly representatives of the genus Oithona which werecharacteristic of a distinct mangrove fauna. Physical forcing influencedthe zooplankton of mangrove estuaries much more than the measured biologicalvariables. The water column was characterised by high concentrations ofparticulate matter, up to 3.3 mg l⁻¹ C and 1.1 mgl⁻¹ N, of low food quality (as indicated by the C:N ratio).Phytoplankton biomass (as chlorophyll a) in all six rivers was on averagefour-fold greater than in neighbouring coastal waters (1.1–12.6µg l⁻¹), and 25% of this chlorophyll a wasderived from cells >10 µm, and thus potentially available tocopepods. The degree of mixing, determined by the combination of tidal stateand the extent of freshwater input, appears to drive both the quantity andquality of particulate material available to higher consumers and thedistribution of zooplankton communities within mangrove estuaries.